The present invention relates to a thermal head mounted on a facsimile machine, a printer or the like.
As shown by FIG. 1, according to a thermal head, a driver IC 3 for selectively generating heat at a heat generating resistor 2 is mounted on an insulative heat generating resistor substrate 1 where a heat generating register row and electrodes for feeding electricity thereto are formed, and a flexible circuit board 4 is electrically connected to the driver IC 3 for transmitting electric signals for operational control and supplying power source from an external circuit. The connection is generally carried out by electrically connecting the flexible circuit board 4 to electrode terminals of the heat generating resistor substrate 1 by soldering or the like. Further, the heat generating resistor substrate 1 and the flexible circuit board 4 are fixed to a radiating plate 5 for excellently radiating heat generated from the heat generating resistor 2.
FIG. 3 and FIG. 4 show an example of the structure of a conventional thermal head. The heat generating resistor substrate 1 and the flexible circuit board 4 are fixed to the radiating plate 5 by using a double-sided tape or an adhering agent. However, when the radiating plate 5 is provided with a structure having a stepped portion, in the case where the fixing operation is carried out by using a double-sided tape or an adhering agent, it is difficult to paste or coat the tape or the adhering agent uniformly over an entire face of the radiating plate in a single operation. Particularly, in the case of the structure having a stepped portion, an adhesive agent cannot be coated by adopting a printing system. As mentioned above, it is ideal that a face of the radiating plate 5 for fixing the heat generating resistor substrate 1 and the flexible circuit board 4 is a plane flush face having no stepped portion and accordingly, as shown by FIG. 3, a stepped difference between the flexible circuit board 4 and the radiating plate 5 caused by the thickness variation of the heat generating resistor substrate 1, has been dealt with by pasting a thickness substrate 6 in correspondence with the stepped difference to the flexible circuit board 4. However, according to this method, the fabrication cost of the flexible circuit board 4 is significantly increased and, therefore, the method has hardly been adopted.
FIG. 4 shows a structure where the radiating plate 5 is provided with a stepped portion. According to the structure, the radiating plate 5 is provided with the stepped difference and accordingly, when the fixing operation is carried out by using a double-sided tape, an operation of pasting the tape at a portion of the radiating plate for pasting with the heat generating resistor substrate 1 and an operation of pasting the tape at a portion of the radiating plate 5 for pasting with the flexible circuit board 4 must be performed separately. Further, in the case of using an adhering agent, as mentioned above, a printing system cannot be adopted and only a coating system by using a brush or the like or an injection system by using a dispenser or the like can be adopted, and therefore, not only the operation is troublesome but also uniform coating is difficult to perform.
According to the example of FIG. 4, there is provided a method in which in respect of the portion of the flexible circuit board 4 for pasting with the radiating plate 5, a double-sided tape is pasted previously on the side of the flexible circuit board 4. In this case, the cost is not as high as that of the structure where the thickness plate 6 in correspondence with the stepped difference is pasted as described above, however, an increase in the cost is unavoidable also in view of a number of steps of operation where operation of detaching exfoliation paper of the double-sided tape is needed and so on.
Accordingly, in either of examples of FIG. 3 and FIG. 4, factors of increasing the fabrication cost of the thermal head are resulted since the flexible circuit substrate 4 becomes expensive or the step of pasting a double-sided tape or the step of coating an adhesive agent becomes complicated.